Quantum Decoherence of the Surface Code: A Generalized Caldeira-Leggett Approach

Abstract

Standard quantum error correction (QEC) models typically assume discrete, Markovian noise, obscuring the continuous quantum nature of physical environments. In this manuscript, we investigate the fundamental limits of an actively corrected surface code coupled to a continuous, un-reset quantum environment at zero and finite temperature. Using the generalized Caldeira-Leggett framework, we map the long-time evolution of the logical qubit to a boundary conformal field theory, establishing an exact equivalence to the anisotropic Kondo model. We evaluate computational times for a finite code distance $L$ for all spatial and temporal correlations. Our analysis reveals that a true thermodynamic threshold exists strictly for short-range environments ($z>1/(s+1)$). In critical or long-range regimes, the macroscopic footprint of the code weaponizes the continuous bath, hindering the topological protection.

18 pages, 5 figures, submitted to the special issue of the Brazilian Journal of Physics "Frontiers in Quantum Mechanics and the 45 Years of the Caldeira-Leggett Model"